The invention relates to a process for producing pulp from fibrous materials, wherein organosilicon compounds are added to the chemical digestion process.
The cellulose fibers and hemicellulose fibers contained in fibrous materials such as wood are held together by lignin, a polymer composed of hydroxyphenylpropane units. The production of pulp, a more or less impure cellulose, involves a separation of lignin from the cellulose. By far the most important process for producing pulp from fibrous material is the process known as the alkaline sulfate process or Kraft process, in which lignin is leached from the fibrous material by an aqueous digesting solution which as its main components contains NaOH and Na2S.
One option of increasing the pulp yield in chemical digestion processes is to add organic surfactants. For example, U.S. Pat. No. 3,909,345 discloses the use of ethylene oxide/propylene oxide block copolymers and U.S. Pat. No. 5,250,152 discloses the use of ethoxylated alcohols and ethoxylated dialkylphenols in the alkaline sulfate process.
It is an object of the invention to provide an improved process for producing pulp from fibrous materials via a chemical digestion process.
The invention relates to a process for producing pulp from fibrous materials, wherein the fibrous materials are reacted with a chemical digesting solution in the presence of organosilicon compounds.
For a given residual lignin content in the pulp, the novel process requires less digesting solution. One measure for the residual lignin content in pulp is the kappa number which corresponds to the consumption of milliliters of 0.1 normal (3.161 g/l) potassium permanganate solution per gram of pulp.
Reducing the amount of digesting solution increases the pulp yield, based on fibrous material used, since smaller amounts of carbohydrates, in particular hemicelluloses, are leached out and therefore smaller amounts of by-products are formed.
If the organosilicon compounds are used, a specific kappa number can also be achieved by the cooking time being shortened.
In the process according to the invention, the kappa number is lowered under constant digestion conditions.
Since the digesting solution now acts to better effect, the pulp contains a smaller amount of relatively coarse, undigested raw fibrous materials (xe2x80x9crejectsxe2x80x9d).
In general, organosilicon compounds result in a higher pulp yield and smaller amounts of undigested fibrous materials.
The organosilicon compounds also improve the mechanical strength factors of pulp and reduce the degradation of cellulose.
Preferred organosilicon compounds are organic siloxanes and silanes which contain an organic polar group and a hydrophobic siloxane moiety or silane moiety and consequently have interface-active characteristics at the phase boundaries liquid/liquid, liquid/gaseous and liquid/solid.
Preferred organosilicon compounds are the organopolysiloxane compounds which are composed of units of the general formulae (I) to (VII)
where
R represents univalent hydrocarbon radicals having from 1 to 18 carbon atoms,
Rxe2x80x2 represents univalent radicals of the general formulae (VIII), (IX), (X) or (XI) 
xe2x80x83in which
R1 represents divalent C1- to C18-hydrocarbon radicals,
R2 represents hydrogen atoms or univalent C1- to C6-alkyl radicals,
R3 represents hydrogen atoms, univalent C1- to C6-acyl radicals, C1- to C6-hydrocarbon radicals, or OSO3X,
X represents hydrogen atoms, alkali metal ions or ammonium ions which may or may not be substituted by C1- to C18-hydrocarbon radicals,
Z represents glycosidyl radicals composed of from 1 to 10 monosaccharide units,
a represents the values 1, 2, 3, 4 or 5,
b represents integer values from 0 to 200,
c represents the values 0 or 1 and
d represents the values 0, 1, 2, 3 or 4,
with the proviso that the organopolysiloxane compounds have at least one unit of the general formulae (V) to (VII).
Likewise preferred organosilicon compounds are the organosilanes of the general formula (XII).
R3SiRxe2x80x2xe2x80x83xe2x80x83(XII)
in which
Rxe2x80x2 represents univalent radicals of the abovementioned general formula (VIII) and
R has the abovementioned meanings.
If b in the general formulae (VIII) to (XI) has a value of at least 2, a may adopt various values within the scope of the formula [O(CR2)a]b of a radical. For example, the scope of the formula [O(CR2)a]b may represent a polyethylene glycol/polypropylene glycol block copolymer.
Examples of hydrocarbon radicals R are alkyl radicals such as the methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, n-pentyl, isopentyl, neopentyl, t-pentyl radical; hexyl radicals such as the n-hexyl radical; heptyl radicals such as the n-heptyl radical; octyl radicals such as the n-octyl radical and isooctyl radicals such as the 2,2,4-trimethylpentyl radical; nonyl radicals such as the n-nonyl radical; decyl radicals such as n-decyl radical; dodecyl radicals such as the n-dodecyl radical; octadecyl radicals such as the n-octadecyl radical; alkenyl radicals such as the vinyl, allyl and the 5-hexen-1-yl radical; cycloalkyl radicals such as cyclopentyl, cyclohexyl, cycloheptyl radicals and methylcyclohexyl radicals; aryl radicals such as the phenyl, naphthyl and anthryl and phenanthryl radical; alkaryl radicals such as o-, m-, p-tolyl radicals, xylyl radicals and ethylphenyl radicals; aralkyl radicals such as the benzyl radical, the xcex1- and the xcex2-phenylethyl radical.
Preferably, at least 90 mol % of the radicals R are methyl, ethyl or phenyl radicals, especially methyl radicals.
Examples of the divalent radicals R1 are saturated straight-chain or branched or cyclic alkylene radicals such as the methylene and ethylene radical and also propylene, butylene, pentylene, hexylene, 2-methylpropylene, cyclohexylene radicals, or unsaturated alkylene or arylene radicals such as the hexenylene radical and phenylene radicals.
Examples of the monovalent alkyl radicals R2 and R3 are listed. under the abovementioned examples of R.
Examples of the hydrocarbon radicals on the ammonium ions in X are the hydrocarbon radicals mentioned for R.
Examples of the C1- to C6-acyl radicals R3 are the acetyl, propionyl and n-butyryl radical.
Examples of monosaccharides of which the glycoside radicals Z may be composed are hexoses and pentoses such as glucose, fructose, galactose, mannose, talose, allose, altrose, idose, arabinose, xylose, lyxose and ribose, glucose being particularly preferred. Preferably, the glycoside radicals Z contain one or two monosaccharide units.
Preferably, a represents the values 2 or 3. Preferably, b represents integer values from 3 to 100, especially from 10 to 70.
Preferably, from 2 to 50% , especially from 5 to 20% of the units of the organopolysiloxane compound have the general formulae (V) to (VII).
Preferably, at least 95% , especially at least 99% of the units of the organopolysiloxane compound are units of the general formulae (II), (VI) and (I). It is also preferred for the organopolysiloxane compound to have an average viscosity of from 20 to 500,00.0 mPaxc2x7s, especially from 200 to 60,000 mPaxc2x7s at 25xc2x0 C.
One organosilicon compound or alternatively mixtures of a plurality of organosilicon compounds can be used.
Preferably, from 0.001 to 1, especially from 0.01 to 0.1 part by weight of organosilicon compounds is used per 100 parts by weight of dry fibrous materials.
Examples of chemical digestion processes which can be used are:
1) The Sulfite Process
The sulfite digestion involves cooking chips with solutions of hydrogen sulfites. Depending on whether the hydrogen sulfite solutions do or do not contain excess sulfur dioxide, the processes are referred to as acid bisulfite processes or simply as bisulfite processes. These are subsumed under the widely established term xe2x80x9csulfite processxe2x80x9d.
2) The Sulfate Process
In the sulfate process the digesting solution, which is also referred to as white liquor, comprises the main components NaOH and Na2S.
The sulfate process is preferred.
If the alkaline sulfate process is used, the process preferably employs from 10 to 35, especially from 20 to 30 parts by weight of Na2O in the form of NaOH per 100 parts by weight of dry wood. The process preferably employs from 3 to 15, especially from 6 to 10 parts by weight of Na2S per 100 parts by weight of dry wood. The process is preferably carried out at from 0.1 to 3 MPa, especially from 0.5 to 1.5 MPa.
The chemical processes can be carried out batchwise or continuously in a pulp digester.
The residence time of the mixture in the pulp digester is preferably from 10 min to 7 h.
Examples of fibrous materials to be used include all those vegetable raw materials (fibrous plants) which have an adequate cellulose content and can be processed with sufficient ease.
Preference is given to the use of wood, one of the raw materials used these days in large amounts in many countries being the wood waste produced in the sawmills. In addition, however, certain annual plants and grasses also play a subordinate part. The wood is used in the form of, for example, chips, shavings or wood dust.
In the following examples, unless stated otherwise,
a) all the amounts given relate to weight;
b) all pressures are 0.10 MPa (abs.);
c) all temperatures are 20xc2x0 C.
d) EO is an ethylene ether unit (xe2x80x94CH2CH2xe2x80x94Oxe2x80x94).